1. Field of the Invention
The present invention is related to brake head assemblies for using in brake beams of railway cars, and more particularly to a pivoting joint for pivotally joining a brake head to a brake beam of a railway car by which an adequate force distribution along the brake shoe and an adequate contact between the brake shoes and the railway car bogie wheels are achieved.
2. Description of the Related Art
Most railroad freight cars and other transportation apparatus use a mechanism called brake rigging, classified generally as either a Body Mounted System (BMS) with an actuator on the car platform; a Truck Mounted System Direct Acting (TMS-DA) with an actuator on the beam; or a Truck Mounted System Indirect Acting (TMS-IA) with an actuator on the transportation apparatus, such as a truck, acting through levers on standard brake beams.
Generally, there is an air reservoir mounted on the car body, which provides pressurized air to at least one brake cylinder. In a BMS, the brake cylinder, in turn, supplies a mechanical force through a system of rods and driving levers to a truck driving lever system, usually consisting of two driving levers and a connecting rod. The driving levers move brake beams, which apply force to the treads of the wheels through interchangeable friction blocks or brake shoes, retarding the rotation of the wheels.
The conventional TMS brake rigging includes two brake beams per truck, at least one brake cylinder assembly per truck, and a driving lever or linkage assembly connected between the brake beams and the cylinder assembly.
There are many brake beam types that may be used in combination with the above-referred conventional brake rigging. One of the most commonly used brake beam types comprises: a compression member; a generally “V”-shaped tension member having its ends coupled to the ends of the compression member; a brake head linked to each end of the compression and/or tension members, each comprising a brake shoe carrier having a brake shoe; two end extensions, each linked at each end of the tension and/or compression member, or hanging means, by which the brake beam is coupled to the bogie of a railway car; and a fulcrum assembly attached to the compression member and tension member, so that the fulcrum remains between the tension and compression members. On the most common TMS-DA, there is also a cylinder assembly mounted in one of the beams, connected to its compression member, while the opposite beam in the same truck has a fulcrum or linkage means on the compression member to transfer the force of the cylinder to both beams, with an automatic double acting slack adjuster element between them, that extends via a trigger to compensate for the wear of the brake shoes.
Normally, the brake heads are fixedly linked to the brake beam by means of bolts passing through perforations located at the ends of the brake beam and through perforations located at the brake heads. Also, the brake heads may be linked to a brake beam by welding the brake head directly to the ends of the brake beam, or are integral to the beam ends as is the case of the cast beams.
The looseness between the extensions of the brake beam and its guides, which is necessary in order to compensate for the movements of the truck components when in operation, causes the brake beam to hang from the truck, so that its non-braking position does not point to the center of the wheel. Furthermore, during the braking operation, due to existent fixed joints between the extensions of the brake beam and its truck guides, between the brake heads and the wheels during the braking operation, and between the brake head and the brake beam, there is a double restriction that somehow buckles the displacement of the beam in the truck guides as well as its self-alignment towards the wheel center, so that the forces applied through the brake head are not transmitted uniformly along the brake shoe, thus producing a non-uniform and incomplete wear of the useful material of the brake shoes, which is a waste of useful material that could be properly used, and therefore, it is necessary to frequently change the brake shoe material which is a waste of time and money. In many occasions this uneven taper wear leaves the shoe material at the bottom of the shoes in as-new condition, while the top has already reached the condemnable limits, thus producing a material waste of approximately 50%.
In extreme cases, the material of the brake shoe is so worn at some points that the metal of the brake shoe carrier comes in direct contact with the corresponding bogie wheel, damaging the brake shoe carrier as well as the wheel.
It is also a common problem that, as the cars run through their cycle life, the components of its brake rigging system gradually wear out, aggravating the conditions of the beam hanging and buckling as referred above, thus further reducing the useful life of the brake shoes as the car ages.
Therefore, it would be desirable to have a brake head which allows a controlled degree of rotation of the brake head about a “z” axis (longitudinal rotation) and about a “y” axis (lateral rotation), so that it allows the brake shoe to pivot over the “z” and “y” axes and thus to completely adapt to the wheel thread.
Considering the above referred problems, the present applicant has developed in the present invention a pivoting joint for pivotally joining a brake head to a brake beam which pivotally joins the brake head to the brake beam in order to allow the brake head to modify its radial and lateral direction with a controlled degree of rotation with respect to the wheel, thus allowing the brake shoe to adapt to the wheel thread and achieving an adequate force distribution along the brake shoe.
The present invention provides a pivoting joint for pivotally joining a brake head to a brake beam, and comprises: means for pivotally joining the pivoting joint to the brake beam for allowing the pivoting joint and the brake head to laterally pivot; means for pivotally joining the brake head to the pivoting joint for allowing the brake head to radially pivot; friction means, cooperating with the means for pivotally joining the brake head to the pivoting linking means, for restricting the movement of the brake head with respect to the pivoting linking means; and mechanical rotation restriction means for restricting the brake head radial rotation angle within a predetermined angular range.
With the pivoting joint of the present invention, all the useful material of the brake shoe is totally used, thus avoiding frequent changes of the brake shoe material, which helps to achieve great money savings in view of the high maintenance costs caused by the frequent changes, and avoiding the waste of useful brake shoe material that still could be used if the thickness of the remaining material were uniform.
Furthermore, thanks to the brake head degree of rotation, torsional forces induced by the levers at certain angles during operation are reduced, thus extending the life of pins, levers, pocket guides, and the beam itself, by avoiding the buckling of the elements, and allowing the rigging system to apply a uniform force to all wheels on the transportation apparatus, such as a truck.